At a very young age, Katsunaga, then known as "Gobomaru", was given in adoption to Toyama Kagetou and his wife, Lady Otsuya, at Iwamura Castle. Lady Otsuya was Oda Nobunaga's aunt. In 1572, the castle was capturedbyTakeda forces under Akiyama Nobutomo, and Gobomaru, then four years old, became a hostage of the Takeda.
In 1581, Takeda Katsuyori released Gobomaru (Katsunaga) to the Oda clan, who returned him to Iwamura Castle, which had been re-taken during his absence.
One year later in 1582, Katsunaga accompanied his father to Honnō-ji. Following the attack on Honno-ji and the death of Nobunaga, Akechi Mitsuhide attacked Nijō Castle, where Nobunaga's son Nobutada was staying. During the fight, Katsunaga was killed and Nobutada committed seppuku.
